Complex formation constants for the aqueous copper(I)-acetonitrile system by a simple general method

A simple spectrophotometric method for the evaluation of formation constants for aqueous copper(I) has been developed, based on the kinetics of reduction of Co(III)(NH(3))(5)X complexes. The method has been applied to the aqueous copper(I)-acetonitrile system to determine the successive formation constants beta(1), beta(2), and beta(3) as 4.3 x 10(2) M(-)(1), 1.0 x 10(4) M(-)(2), and 2.0 x 10(4) M(-)(3), respectively, in 0.14 M NaClO(4)/HClO(4) at 21 +/- 1 degrees C.     

A Cu/Cinchona P,N-ligand system enabled general asymmetric C(sp~3)–C(sp) coupling

正Due to the special structural feature and versatile reactivity towards various types of transformations, alkynes have inspired continuous research interest for their generation, incorporation and application in organic synthesis, chemical biology and material science [1]. Notably, since its invention in 1975, the Sonogashira reaction, which efficiently couples aryl halides with aryl or vinyl terminal alkynes via Pd(0)/Cu(I) synergistic catalysis, has proven to be one of the most     

NAD(P)+-NAD(P)H models. 90. Stereoselection controlled by electronic effect of a carbonyl group in oxidation of NAD(P)H analog

4-Monodeuterated NAD(P)H model compounds (1,4,6,7-tetrahydro-1,6,11-trimethyl-5-oxo-5H-benzo[c]pyrido[2,3-e]az epin; 11Me-MMPAH) have been oxidized with a series of p-benzoquinone and its derivatives in the presence of Mg2+. The models have an axial chirality with respect to the orientation of carbonyl dipole, the dihedral angle of which is larger than 55 degrees out of the plane of dihydropyridine ring. Without Mg2+, the anti- (with respect to the carbonyl dipole) hydrogen is 3 to 32 times more reactive than the corresponding syn-hydrogen, whereas, when Mg2+ is present in the system, the selectivity is shifted toward the syn-preferency. Mg2+ plays the role of a Lewis acid catalyst to control the stereochemistry at the same time as it catalyzes the reaction.     

Study of internal rotation of the vinyl group in 1-, vinylpyridones by the AM-1 method

By the AM-1 method in the semirigid model approximation, the potential energy of internal rotation of the vinyl group has been calculated for 1-vinyl-2-pyridone, 1-vinyl-6-methyl-2-pyridone, and 1-vinyl-4-pyridone. The potential energy of internal rotation in the first and third of these molecules has two minima corresponding to torsion angles around the N-C bond approximately 0 and 180°, separated by barriers to internal rotation 3.99 and 2.94 kcal/mole, respectively. For the 1-vinyl-2-pyridone, the energy minimum at =180°, the s-cis(O) conformation, is 1.83 kcal/mole above the first minimum. For the 1-vinyl-6-methyl-2-pyridone, the torsion angles 0 and 180° correspond to energy maxima; the energy minima occur at 35° and 140°. In the harmonic oscillator approximation, the intervals of torsional vibrations of the vinyl group in these comopunds have been estimated. Data from the AM-1 calculation are in qualitative agreement with the available¹H and¹³C NMR data on the structure of 1-vinyl-2-pyridone, 1-vinyl-5-methyl-2-pyridone, and 1-vinyl-4-pyridone.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1367–1372, June, 1991.     

Analysis of influence of the 5-methyl group on internal rotation of the vinyl group in 1-vinylpyrazoles,by the AM-1 method

According to results obtained in quantum-chemical calculations by the AM-1 method, 1-vinyl- and 1-vinyl-5-methylpyrazole may exist in the s-cis(N₂) and s-trans(N₂) conformations. The introduction of the CH₃ group into position 5 of the pyrazole ring gives a substantial increase in population of the s-cis form, and also increases the interval of torsional vibrations of the vinyl group around the equilibrium position.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2077–2079, September, 1991.     

Unitary group approach to general system partitioning. II. U(n) matrix element evaluation in a composite basis

An explicit segment level formalism is derived for the matrix elements of the U(n) generators in an arbitrary (multishell) composite basis. The results of this paper, which contain the usual (spin-independent) unitary calculus approach as a limiting case, yield a more powerful and versatile algorithm than the traditional (spin-independent) unitary group formalism.     

A general and efficient method for the preparation of unsymmetrical bidentate P,N and P,S ligands

A general and efficient preparation of chiral and achiral P,N and P,S ligands is described where ligands are prepared by reacting a variety of 2- or α-lithio N- or S-heterocycles and a lithiated phosphine with 1,2-cyclic sulfates.     

Lipophilicity assessment of basic drugs (log P(o/w) determination) by a chromatographic method

A previously reported chromatographic method to determine the 1-octanol/water partition coefficient (log P(o/w)) of organic compounds is used to estimate the hydrophobicity of bases, mainly commercial drugs with diverse chemical nature and pK(a) values higher than 9. For that reason, mobile phases buffered at high pH to avoid the ionization of the solutes and three different columns (Phenomenex Gemini NX, Waters XTerra RP-18 and Waters XTerra MS C(18)) with appropriate alkaline-resistant stationary phases have been used. Non-ionizable substances studied in previous works were also included in the set of compounds to evaluate the consistency of the method. The results showed that all the columns provide good estimations of the log P(o/w) for most of the compounds included in this study. The Gemini NX column has been selected to calculate log P(o/w) values of the set of studied drugs, and really good correlations between the determined log P(o/w) values and those considered as reference were obtained, proving the ability of the procedure for the lipophilicity assessment of bioactive compounds with very different structures and functionalities.     

In silico binding free energy predictability by using the linear interaction energy (LIE) method: bromobenzimidazole CK2 inhibitors as a case study

Protein kinase CK2 is essential for cell viability, and its control regards a broad series of cellular events such as gene expression, RNA, and protein synthesis. Evidence of its involvement in tumor development and viral replication indicates CK2 as a potential target of antineoplastic and antiviral drugs. In this study the Linear Interaction Energy (LIE) Method with the Surface Generalized Born (SGB) continuum solvation model was used to study several bromobenzimidazole CK2 inhibitors. This methodology, developed by Aqvist, finds a plausible compromise between accuracy and computational speed in evaluating binding free energy (DeltaGbind) values. In this study, two different free binding energy models, named "CK2scoreA" and "CK2scoreB", were developed using 22 inhibitors as the training set in a stepwise approach useful to appropriately select both the tautomeric form and the starting binding position of each inhibitor. Both models are statistically acceptable. Indeed, the better one is characterized by a correlation coefficient (r2) of 0.81, and the predictive accuracy was 0.65 kcal/mol. The corresponding validation, using an external test set of 16 analogs, showed a correlation coefficient (q2) of 0.68 and a prediction root-mean-square error of 0.78 kcal/mol. In this case, the LIE approach has been proved to be an efficient methodology to rationalize the difference of activity, the key interactions, and the different possible binding modes of this specific class of potent CK2 inhibitors.     

NAD(P)+–NAD(P)H models. 84. Stereochemistry controlled by the electronic effect from a sulfinyl group

2,3-Dihydro-2,2,4-trimethylthieno[3,2-b]pyridinium 1-oxide iodide ( 1 ) has been reacted with various inorganic and organic hydride donors. It has been found that the stereochemistry of reaction is controlled by the orientation of the sulfinyl dipole, and the relative bulkiness of substituents plays no role in determining the reaction face: a reactive hydride donor prefers to attack at the anti-face with respect to the sulfinyl dipole, whereas a less reactive hydride donor prefers to attack at the syn-face.     

Estimation of boiling and melting points of light,heavy and complex hydrocarbons by means of a modified group vector space method

A modified group vector space (GVS) method was developed for estimating the normal boiling points and melting points of alkanes, alkenes, alkynes, and cyclic and aromatic hydrocarbons including their isomers. The present method, based on group contributions as well as topological contributions, can represent the normal boiling points of isomeric compounds accurately. The group parameters for the modified GVS method were obtained from the correlation of the boiling and melting points of 1115 hydrocarbons.     

Four types of relaxation in chemical kinetics (linear case)

According to results obtained previously for the linear equations of chemical kinetics, the relation between the steady-state reaction rate and the relaxation time has been studied.

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